825 Foot Deep Well

I have an 825 foot deep well. The well driller feels that the recovery rate of the well at 825 feet is 5 to 6 gpm. The well has a deep static level around 400 feet. At present my 3/4 hp pump is set at the max depth of 425 +/- I believe. I frequently run out of water with just a shower or two and basic water use. My driller said that my best option to solve my water problem was to install a cistern at the cost of around $2,200.00. To install a pump at the bottom of my well he said would cost 8 to 9 thousand dollars because of not only the size of the pump, but he would have to use steel piping to the bottom of the well because of the weight of the piping, water, and pump. I have a friend that lives down south in Virginia, and he said that down there for a deep well like this that they would still use plastic water pipe, but would hang the whole thing off a stainless steel cable so to support the weight. I was wondering if anyone had heard of this being done in the past. Also any ideas as to what really is the best way for me to get at the water in the bottom of my well.

Information on my well

825 Feet deep

5 - 6 gpm recovery at 825 feet.

Static level... Not totally certain but present pump set at 425 feet and quickly run out of water.

Feeding a 2 story house with 2 bathrooms. Family of 4

Well about 75 feet from house.

I think Sch 120 PVC pipe will go that deep but, it is probably as expensive as steel pipe. It is not just the weight of the 825' string but, the pressure at the bottom. There will be about 400 PSI on the bottom pipe when the water level pulls down and you are still getting 50 PSI in the house. My book shows sch 120 in 1" pipe is good to 700' and 50 PSI in the house. I don't think you will need to go all the way to 800'. Depending on the size of the well casing, the well should store about 1.5 gallons per foot. So just going down to 625' will give you an extra 300 gallons of storage.

The cable thing with lesser pipe is not a good idea. The lesser strength pipe won't handle the pressure. If the pipe or the cable break, it can wedge in the well, which is what we call planting a pump. In other words you would just have to drill a new well if this happens. (Not good)

I still like putting the pump deeper instead of the cistern idea. The water in the well will stay cool and fresh, where the water in a cistern can get stale and need chlorination to keep from being contaminated. Then you would also need a 2 pump system, which is twice the equipment to purchase and maintain.

What pressure tank(s) are in the setup?

1" Schedule 80 PVC is rated at 378 psi (873 ft) at 73 F. It should be about 10% greater at the temperature you are likely to find in a well.

A Harvel site shows 630 psi maximum working pressure with asterisks for which I can't find the corresponding footnote.
http://www.harvel.com/pipepvc-sch40-80-dim.asp

Manufacturers recommend a 50% reduction in allowable pressure for threaded fittings.

It would be possible to lay out the pipe and cement the joints on the ground prior to installation. You would need equipment that would permit a large bending radius during installation.

You could use a 2 HP/5 GPM Goulds 5GS20 pump that would deliver about 3 GPM to your pressure tank from 800 ft.

pressure

The pressure in the pipe is determined by the distance between the water level in the well and the distance to the storage tank level, plus the system's operating pressure. NOT the depth of the pump. If the well cannot recover as the water is being withdrawn, then you would need an intermediate storage container.

Bob NH said:

1" Schedule 80 PVC is rated at 378 psi (873 ft) at 73 F.
Manufacturers recommend a 50% reduction in allowable pressure for threaded fittings.

It would be possible to lay out the pipe and cement the joints on the ground prior to installation.

Click to expand...

Sch 80 PVC could handle the pressure but, I am not sure about the weight. You would never want to use a glue joint down the well, especially a well this deep.

Various sites give maximum pressure ratings. The ones at the links below gives 630 psi for 1" schedule 80.
http://www.sd-w.com/civil/pipe_data.htm

http://www.us.piping.georgefischer.com/external/us_handbook/03.pdf

I calculated the weight of water, pipe, and pump at about 675 pounds.

With head of pump at depth + 100 ft the total axial load on the pipe is about 700 pounds (don't count weight of water + pressure).

Hoop stress in pipe due to pressure is 1300 psi.

Axial stress due to weight and pressure is 1100 psi.

Minimum tensile strength of the material is 7200 psi. (Factor of safety more than 5 for pressure, factor of safety of more than 6 for axial load). Reported other places as high as 7450 psi.

Shear stress in minimum socket bond = 150 psi This is pretty low and is not likely to be the failure location for properly installed pipe.

Threaded joints are weaker than cemented joints because of the smaller area at the root of the male threads. Also, the notch at the root can originate cracks. Most pipe manufacturers recommend half the pressure for threaded joints. One could make up male/female adapters and screw the pipe together as it is installed. The male adapters usually have slightly smaller bore but the pressure loss at 5 GPM would be insignificant.

So 1" Schedule 80 PVC will work in an 800 ft well. I would have it done by someone with a rig that could intall cemented joint pipe, or make up the pipe with male and female adapters.

I am sorry Bob but, I would never glue any pipe in the well, or use male and female adapters. I have had to fish out too many pumps that were dropped in the well by someone who thought this was a good idea.

Me too. You should stay with Engineering Bob and leave the Well Installations to us. I don't care what your Engineering books say, trust me, Glued Joints don't work.

bob...

Valveman and Speedbump are right. No Glue!

I've set many pumps to 700 ft. on schedule 80 threaded PVC in New Mexico. However we used heavy duty brass or stainless steel couplings. No rope or steel cable.

valveman said:

I am sorry Bob but, I would never glue any pipe in the well, or use male and female adapters. I have had to fish out too many pumps that were dropped in the well by someone who thought this was a good idea.

Click to expand...

speedbump said:

Me too. You should stay with Engineering Bob and leave the Well Installations to us. I don't care what your Engineering books say, trust me, Glued Joints don't work.

bob...

Click to expand...

Porky said:

I've set many pumps to 700 ft. on schedule 80 threaded PVC in New Mexico. However we used heavy duty brass or stainless steel couplings. No rope or steel cable.

Click to expand...

If I were having failures when making joints in accordance with the manufacturers specifications I would figure out what I was doing wrong.

The manufacturers of the pipe say that threading the pipe requires a 50% reduction in the pressure rating.

If I am the owner of a well, and there is a failure of a system installed contrary to the manufacturers requirements and warnings, I would be all over the installer insisting that he restore the well, pump, and installation at no cost to me.

From the following link: http://www.harvel.com/tech-specs-pvc-pipe-80.asp Emphasis by Harvel (the manufacturer)
"Thread only Schedule 80 or heavier walls. Threading requires a 50% reduction in pressure rating stated for plain end pipe @73F. Threading of Schedule 40 PVC pipe is not a recommended practice due to insufficient wall thickness."

Bob NH said:

If I am the owner of a well, and there is a failure of a system installed contrary to the manufacturers requirements and warnings, I would be all over the installer insisting that he restore the well, pump, and installation at no cost to me.

Click to expand...

Exactly Bob, we would all stand behind our work 100%. That is why we would never glue pipe that went down a well. We would end up having to drill the people a new well, replace the pump, and everything else needed to restore the water system properly, at no charge.

I also like to use sch 80 threaded PVC with brass or galv couplings. I would never thread sch 40, or use male and female adapters. Settings to a maximum of about 400', I only use the standard, not the long couplings. I would certainly use the long couplings if the well was deeper, as Porky described.

I would also thread this pipe together dry, with no thread compounds of any kind, and I would know when it made a popping noise that it was tight enough. I also know that this kind of pipe has a bursting strength of 2.5 to 2.7 times the rated pressure. So I am not worried about the 50% reduction thing.

These are the kinds of things that the manufacturer won't tell you because he doesn't know this stuff. Everything a pump man or driller knows is learned the hard way. We listen to the manufacturer, and then we start trying to figure out how to make it work for real.

When we get into trouble is when we have to do things exactly as the customer or engineer tells us to do. We end up taking the blame and paying the price, and we knew better when we let them talk us into it. That is why good pump men do pretty much just like their father and grandfather did. Anytime we let someone talk us into doing something different, it cost us big time. Anytime you don't listen to us, it should cost you big time but, it usually doesn't. Wonder why most people in this business are usually so grumpy?

You can read all the Manufacturers Specs you like and you can try them out all you like as we already have. Then you find that we do things the way we do, because this is the way that it works the best. Not because of the limited testing done by the Manufacturer, but by all the problems we had by following his specs. The same goes with Engineered Drawings and Specs. We take them out into the field, try them out and make corrections per our experience and make them work the way they were intended. Then the Engineers get to take all the glory for having designed the perfect Mouse Trap.

bob...

glued joints that depth is mental. we have used a pipe called centra lock from usa on quite deep holes it uses o rings and nylon cords. or galv steel on those depths you would need flanged pipes.

i cant belive a 3/4 hp pump would be the right choice of pump. do you have 3phase electric?

i also cant see how the yeild was tested at 825 feet at such a slow rate and the pump is sitting so much higher it must be even worse that high up.

it just does not all add up.

tank the water instead of the hassle of going lower then pump it from there.

I agree. And the Certa-Lok by CertainTeed is some really good stuff for deep holes.

Forgive my ignorance, but when you say you only use threaded joints, how do the threads get there? Does Sch 80 pipe come threaded? What does a "sch 80 threaded PVC with brass or galv couplings" joint look like?

You can get threaded male ends on sch 40 or 80 PVC; the same as galvanized pipe. It is made that way.

The couplers to put two pieces together are threaded female and you screw them onto the end of the pipe; instead of 'gluing' them. They look like a solvent weld coupler but have threads.

I don't like the plastic threaded couplings. They have a tendancy of coming unscrewed from the starting torque of the motor. Just rgular Galv., Brass, or Stainless Steel couplings will thread right on. Not much meat left when you thread sch 40, I wouldn't do it in a well.

hj said:

The pressure in the pipe is determined by the distance between the water level in the well and the distance to the storage tank level, plus the system's operating pressure. NOT the depth of the pump. If the well cannot recover as the water is being withdrawn, then you would need an intermediate storage container.

Click to expand...

But the well water level can be sucked down to the level of the pump and thus you would want the pipe to be able to handle the worst case pressure.

The water level is the dynamic level when the pump is running. The static level has absolutely no bearing on the pressure the pipe has to endure.

hj said:

The pressure in the pipe is determined by the distance between the water level in the well and the distance to the storage tank level, plus the system's operating pressure. NOT the depth of the pump. If the well cannot recover as the water is being withdrawn, then you would need an intermediate storage container.

Click to expand...

It is unless you put in a CSV, in which case the pressure from the pump to the top of the water in the well is the pressure that the pump will develop at 1 GPM; which is virtually the shutoff head of the pump.